Nowadays the best investment is that you hold that amount in your wallet as in the next month the halving will occur and with that the price will increase much faster and o a higher value.
You can try to take part in some of these campaigns at this forum that will give you a chance to earn some free bitcoin because you cannot do much with only $20 worth of Bitcoin.
Or you can try Bitcoin gambling maybe luck is on your side and you can make more Bitcoin.